input-panel: Bounce the input panel slide

A little bit over the top, but fun.  We may want to make a weston.ini key
for this eventually.
diff --git a/src/animation.c b/src/animation.c
index 782df24..a93d26e 100644
--- a/src/animation.c
+++ b/src/animation.c
@@ -303,8 +303,9 @@
 	if (!animation)
 		return NULL;
 
-	animation->spring.friction = 900;
-	animation->spring.k = 300;
+	animation->spring.friction = 600;
+	animation->spring.k = 400;
+	animation->spring.clip = WESTON_SPRING_BOUNCE;
 
 	return animation;
 }